The present invention relates to mass spectrometry and a mass spectrometry system, and in particular, to a mass spectrometer and a system for analyzing a mass spectrum in which biopolymeric substances such as protein, polypeptide, sugar, and nucleic acid are identified and are quantitatively determined with high precision and high throughput.
As protein identifying an determining methods utilizing a mass spectrometer (MS), a technique using isotope labeling has recently attracted attention. According to the technique, samples including a first sample and a second sample are obtained respectively from two test bodies, i.e., a first test body and a second test body. The first sample is bonded or combined with a “light reagent” and the second sample is combined with a “heavy reagent”. The heavy and light reagents are equal in chemical structure. However, these reagents differ in the mass number from each other and hence are different in the molecular weight from each other.
When the first and second samples are mixed with each other and the mixture is measured by a mass spectrometer, there appear a pair of peaks apart from each other by difference (Δm) between the molecular weight values. If the first and second protein samples are attained respectively from the same test body and the samples are substantially equal in density and quantity to each other, the two peaks associated with the respective samples have substantially the same intensity. However, if a first sample is obtained from a sick test body and a second sample is attained from a healthy test body, there possibly appear a pair of peaks having mutually different peak intensity depending on cases.
By analyzing such peaks, it is possible to determine protein as a marker of a disease. The peak analysis is also expected to facilitate clarification of various protein functions.
The techniques using isotope labeling have been described in many articles, for example, JP-A-2003-107066 and Japanese Patent No. 3345401. The articles describe a method in which a reagent marked by an isotope is added to a measuring sample and the sample is analyzed by a tandem mass spectrometer capable of achieving multistage dissociation and measurement. There is also described a method in which by uses of an intensity ratio of the peak pair detected through a first-stage measurement (to be abbreviated as MS1 hereinbelow), a second-stage measurement (to be abbreviated as MS2 hereinbelow) is conducted to determine a protein array.
Description will now be given of a problem in the prior art. The tandem mass spectrometer can achieve multistage dissociation and measurement through one measuring session. Ordinarily, from peaks measured by MS1, peaks required to identify an amino acid array are selected to conduct MS2. By achieving database retrieval, an amino acid array corresponding to the MS2 spectrum measured by MS2 is determined. According to the measuring apparatus of the present stage of art, if the mass number associated with the “necessary peak” is known, a peak to be selected by MS1 can be registered to the apparatus. Therefore, the dissociation and measurement up to MS2 can be automatically carried out through one session.
If the mass number is unknown, MS1 is first conducted to select a peak for MS2. That is, the MS2 spectrum is acquired through measurement in the second session. In an ordinary case, a liquid chromatograph (to be abbreviated as LC hereinbelow) is installed in a stage preceding the mass spectrometer. Constituent elements or components flown from the LC are used as a sample for the mass spectrometer. In the separation by the LC, a period of time of several seconds is required to obtain the elements to be measured depending on cases. The elements flow from a column of the LC for about ten seconds to 20 seconds. Therefore, if it is not possible that the MS1 results are analyzed and the peak obtained by MS2 is judged within the period of about ten seconds to 20 seconds, the time-consuming separation is required to be conducted by the LC. Additionally, since it is likely that composition of the constituent elements for the measurement vary between when the flow of the elements is started and when the flow thereof is stopped. Consequently, the peak thus measured is favorably selected within a period of time from about 0.1 second to one second.
In conjunction with the conventional method, description has not been given of a system in which the MS1 spectrum is analyzed and a peak to be measured by MS2 in such a short period of time, i.e., from about ten seconds to about 20 seconds. Therefore, in the method of prior art, for a sample for which a relationship between a mass number and occurrence of a peak pair having intensity ratio difference is known, an amino acid array of protein can be identified through at least one measurement session. However, for a sample for which the relationship is unknown, at least two measurement sessions are required to identify an amino acid array of protein. Since the throughput of LC is slow in general (about several hours), when the number of measurement sessions increases, the throughput including the identification of an amino acid array is considerably reduced. It can be considered that a need for rapid identification and quantitative determination increases in the future for, for example, application thereof to a diagnosis and medical treatment. This requires to remove any factors which lower the throughput.